CHRONIC OBSTRUCTIVE PULMONARY DISEASE (COPD)

COPD is characterized by the progressive development of airway limitation that is not fully reversible.

The term COPD encompasses chronic bronchitis and emphysema.

     Chronic bronchitis is defined as the presence of a productive cough for more than 3 months for more than 2 successive years.

     Chronic bronchitis follows prolonged exposure of the airways to non specific irritant and characterized by hypersecretion of mucous and inflammatory changes in the bronchi.

     Pulmonary emphysema is defined as enlargement of air spaces and destruction of lung parenchyma, loss of lung elasticity, and closure of small airways. Obstruction to expiratory airflow can also lead to the formation of bullae with compression of the adjacent lung tissues.

Diagnostic and Clinical Features

A chronic productive cough and progressive exercise limitation are the hallmarks of persistent expiratory airflow obstruction.

Patient with predominant chronic bronchitis present with chronic productive cough, whereas patient with predominant emphysema complain of dyspnea

                                                           Chronic bronchitis                                           emphysema

Mechanism of airway             decreased airway lumen due                         loss of elastic recoil of the

Obstruction                              to mucous and inflammation                         lung

Dyspnea                                    moderate                                                           severe

FEV₁                                            decreased                                                          decreased

PaO2                                          marked decrease                                              moderate decrease

                                                    (blue bloater)                                                    (pink buffer)

PaCO2                                        increased                                                            normal - decrease

Diffusing Capacity                    normal                                                                decreased

HT                                               increased                                                            normal

Corpulmonale                           marked                                                                mild

Prognosis                                   poor                                                                     good

Pulmonary Function tests

Pulmonary Function tests reveal

1.       Decrease in FEV₁ / FVC ration

2.       Decrease in F. expiratory flow

3.       Increase in RV and normal to increase FRC, TLC

Chest Radiography

Radiologic abnormalities may be minimal but it meight show

·         Hyperlucency and hyperinflation

·         Flattening of the diaphragm

·         Very vertical cardiac silhouette

·         Emphasematous bullae

ABG

ABG can be used to categorize patient with COPD as

Pink buffers

PaO2 usually high than 60mmHg and PaO2 is normal

Individual characterized as pink buffers are typically thin and free of signs of right heart failure and have severe emphysema.

Blue bloaters

PaO2 usually less than 60mmHg and

PaCO2 chronically increased to more than 45mm

Blue bloater typically exhibit cough and sputum production

Consequences of these two Arterial BIood  Gas pattern

Blue bloater:

Arterial hypoxemia and respiratory acidosis lead to increase in pulmonary vascular resistance with resultant pulmonary  hypertension.

Chronic pulmonary hypertension cause right ventricular hypertrophy and failure (Cor pulmonale) arterial hypoxemia also cause secondary erythrocytosis.

Pink buffers:

Loss of pulmonary cap. Vascular bed decrease

Lung diffusing capacity.

Since paO2 is only mildly decrease, pulmonary V.C. is minimal and erythrocytosis does not occur.

Spirometric Classification of COPD

0:     at risk        normal spirometry

                           Chronic sympt

                           FEV₁ / FVC    ˂   70%

I:     mild            FEV₁ ≥ 80% of predicted

                           with or without chronic symptoms

II:    moderate FEV₁ / FVC  ˂ 70%

                          50% ˂ FEV₁  ˂ 80%

                          with or without symptoms

III: severe                       FEV₁ / FVC ˂ 70%

                                        FEV₁  30-50% of predicted

                                        With or without chronic symptoms

IV:  very severe             FEV₁ / FVC  ˂  70%

                                        FEV₁  ˂  30%

                                        FEV₁  ˂  50% + chronic respiratory failure

Treatment of COPD

1.       Cessation of smoking and supplemental O2

2.       Drug therapy

-          Bronchodilator, β agonist, anticholinergic, antibiotics

3.       Lung volume reduction surgery

Anesthetic management of patient with COPD

Preoperative management

The history and physical examination of patient with COPD provide more accurate assessment of the likelihood of post-op pulmonary complications.

A history of poor exercise tolerance, chronic cough or unexplained dyspnea combined with diminished breath sounds, wheezing and prolonged expiratory phase predict an increased risk of post-op pulmonary complications.

Preop pulmonary Functions  tests

The results of pulmonary function tests and ABG can be useful for predicting pulmonary function after lung resection but they do not reliably predict the likelihood of post-op pulmonary complications after non-thoracic surgery.

Indications for pre-op tests typically include:

1.       Hypoxemia on room air or the need for home oxygen therapy without a known etiology

2.       Bicarbonate more than 33mEq/L or PaCO2 ˃ 50mmHg

3.       History of respiratory failure

4.       Severe shortness of breath due to respiratory disease

5.       Planned pneumonectomy

6.       Determining the response to bronchodilator

7.       Suspected pulmonary hypertension

Risk reduction strategies

1.        Preoperative

-          Encourage cessation of smoking for at least 6 weeks

-          Treat evidence of expiratory airflow obstruction

-          Treat respiratory infection with antibiotics

-          Patient education regarding lung expansion maneuver’s

2.       Intraoperative

-          Use of minimally invasive surgical technique

-          Consider use of regional anesthesia

-          Avoid prolonged surgery ˃ 3 hours

3.       Postoperative

-          Institute lung expansion maneuvers (voluntary deep breathing, incentive spyrometry, CPAP)

-          Maximize analgesia

Acute effects of smoking cessation

The adverse effects of CO on oxygen carrying capacity and effects of nicotine on the cardiovascular system are short lived.

-          The elimination half life of CO2 is approximately 4-6h when breathing room air.

Within 12h after cessation of smoking the PaO2 at which Hb is 50% saturated increase from 22.9 to 26.4mmHg and plasma level of carboxyHb decrease from 6.5% to 1%

-          The sympathomimetic effects of nicotine on the heart are transient, lasting only 20-30mins.

-          Other long term benefits of smoking cessation include: improvement in ciliary function, decrease in sputum production

Intraoperative management

Regional anesthesia is suitable for lower intra-abdominal and lower extremities procedures. However, regional anesthetic techniques that produce sensory anesthesia above T6 are not recommended as they may impair the ventilatory functions requiring active exhalation such as expiratory reserve volume, peak expiratory flow and maximum minute ventilation. Clinically this is manifested as a cough that is inadequate to clear airway secretions.

Loss of proporioception from the chest, and unusual position like lithotomy or lateral position, often accentuate dyspnea in awake patient.

It must be appreciated that COPD patient can be extremely sensitive to the ventilator depressed effects of sedative drugs. When used, it should be given in small incremental doses.

-          General Anesthesia

General anesthesia is often provided with volatile anesthetics. Volatile anesthetics produce bronchodilatation and have ability to be rapidly eliminated through the lung minimizing postop resifual ventilator depression.

Nitrous oxide should be avoided in patient with bullae and patient with pulmonary hypertension. Opioids may be less desirable as they cause prolonged postop respiratory depression.

Ventilation should be controlled with small moderate tidal volume and slow rates to avoid air trapping humidification of inspired gases and use of low gas flow help to keep airway secretion moist.

Arterial CO2 measurement should be used to guide ventilation. Ventilation should be adjusted to maintain a normal arterial pH.

Hemodynamic onitoring should be dictated by any underlying cardiac dysfunction and the extent of surgery.

Postoperative management

Lung expansion maneuvers

They decrease the risk of atelectasis by increasing lung volumes.

They include:

Deep breathing exercises

Chest physiotherapy

Incentive spirometry

Positive pressure breathing techniques

Pain control

Postop. Neuroaxial analgesia with opioids may permit early tracheal extubation, early ambulation, which help to increase FRC and improve oxygenation.

Postoperative neuroaxial analgesia is recommended after high risk thoracic abdominal and major vascular surgery.

Mechanical ventilation

Continued mechanical ventilation during the immediate postop period may be necessary in patient with severe COPD who have undergone major abdominal or intra-thoracic surgery.

FiO2 and ventilator settings should be adjusted to maintain paO2 60-100mmHG and paCO2 in a range that maintains pH at 7.35 – 7.45.

The decision to discontinue mechanical ventilation and tracheal extubation is based on the patient clinical status and indices of pulmonary function.